The present invention relates to an optical disk which is used to a record data and, more particularly, to system and method for managing recording areas on a writable type optical disk which is used in a data file apparatus or the like for a computer.
Hitherto, as an external memory medium for a computer, a writable magnetic recording medium such as floppy disk, hard disk, or the like has been used. In recent years, the use of an optical disk having a large memory capacity of hundreds of megabytes or more has begun as an external memory medium for a computer. On the other hand, in association with the advancement of the optical disk technique, the use of not only the read only type or WORM type optical disk but also the writable type optical disk has been studied.
The phase transition type optical disk and the magneto-optical disk have been developed constitute present writable type optical disks. However, such disks have several problems. Particularly, there are problems such that the overwriting technique is not completed yet, the reliability of the disk is not very high, the seeking time is long (the access speed is slow), and the like. With respect to the overwriting technique, the development including the phase transition type optical disk has progressed somewhat. However, it does not reach the practical use stage yet. In the present technique, the processing speed is slow because in order to rewrite data, the system must wait until the disk rotates once to erase the data which has already been written, and thereafter, new data is rewritten.
On the other hand, the slower seeking time as compared with that in the case of the magnetic medium becomes a large cause of employing the necessity of a managing system different from that for the magnetic medium as a managing system of the optical disk. Further, in terms of reliability as well, there remains a problem of deterioration of the disk such that a difference of error rate occurs due to the frequent rewritting operations, or the like.
As an example of an application as an external memory device for a computer, a managing system similar to that for the ordinary magnetic medium is used from an operating system by using the rewritable characteristic.
A managing system of the magnetic medium type will now be described with reference to FIGS. 3 and 4. In the managing system of the magnetic medium type, the area in the medium is divided into a plurality of areas of a predetermined size and the areas are managed by using a table for recording the connecting state of a discontinuous file which exists in the blank area or a plurality of areas every area. Each of the areas is constructed on a block unit basis of a fixed length size of ordinarily about a few kilobytes. FIG. 3 shows such a table comprising file area management information 312 to record files and blank area management information 311 to manage the recordable blank areas. File name managing means 308 manages the file recording blocks on the basis of the file area management information 312. Recording position deciding means 309 decides the recording position on the basis of the blank area management information 311 in the case where a file is additionally recorded. Since data can be overwritten onto the magnetic medium, there is no need to wait for the rotation of the disk to erase as in the case of the optical disk. Therefore, the operating system has no need to discriminate whether the area to record a file is the area which has previously been used or the area from which data has already been erased (including a virgin area). The recording position deciding means 309 assigns the blank area to record a file by using an algorithm shown in FIG. 4.
In step 401 in FIG. 4, the blank areas are sequentially searched from the low address side by using the blank area management information 311. In step 402, on the basis of the result of step 401, if a blank area exists, step 403 follows and if no blank area exists, this is considered as indicating that a recording error occurs due to the area overflow, and the processing routine is finished. In step 403, the overwriting into the blank area searched in step 401 and the verification are instructed to an optical disk control section 306. In step 404, a check is made to see if the whole file has been recorded, or not. If a not-recorded portion still exists, the processing routine from step 401 is repeated.
However, the problem of the processing speed occurs in the case where the algorithm of FIG. 4 is applied to the writable type optical disk in which the overwriting operation cannot be performed. In the algorithm of FIG. 4, the blank area which needs the erasing process and has previously been used on the low address side is preferentially assigned. Therefore, the recording processing speed becomes slow as compared with the case of assigning the blank area from which data has already been erased on the high address side.
Further, according to the magnetic medium type managing system, since the blank areas are managed on a block unit basis, in particular, there is a problem of the recording area management such as release or reuse of the recording area. For instance, the released blank blocks of a small size discretely exist due to the deletion, addition, or the like of the file. In the case of newly adding a file to the medium in such a using state, in general, the operating system searches the blank block from the low address side and sequentially records a part of the file, so that the file is divided into a plurality of blocks and discretely exists in the medium.
On the other hand, in the optical disk of a slow access time, it is desired to continuously record data. This is because the reproducing processing efficiency can be fairly improved since the extra seeking operation is prevented and a plurality of sectors can be read out in a lump upon reproduction of the file. Therefore, in the managing method of the magnetic medium type, there are problems such that the file content is distributed, it takes a time to move the head or to rotate the disk upon reading of the file, the reproducing processing speed becomes extremely slow, and the like, so that such a method is improper as a managing system of the optical disk.
In addition, in the case of also commonly using the magnetic medium type managing system, a problem of deterioration of the disk also occurs. For instance, each time the file is updated, the rewriting operations frequently occur for the fixed area in which area management information or the like is recorded. Therefore, the number of rewriting times of only a special block in the optical disk remarkably increases, the difference of frequency of the local rewriting operations occurs, and such a difference can easily become a cause of the difference of error rate. Particularly, the significant information such as area management information to manage the whole optical disk is frequently recorded in the fixed area on the medium in order to first read out such information when the system is set. If such management information is obstructed, there is a great risk that the whole medium cannot be used.